To fill their top spot on the House Judiciary Committee, Democrats had a choice between experts in two critical policy arenas — a constitutional-law ace with firsthand experience battling Donald Trump, and an architect of sweeping immigration legislation.

By a wide margin, they chose the constitutional-law expert. Why? To ready themselves for a battle with President Trump that could end with impeachment proceedings.

The selection of Rep. Jerrold Nadler (D-N.Y.) as the ranking Democrat on the Judiciary Committee was the clearest sign yet of how seriously House Democrats consider the possibility of a full-blown constitutional showdown with Trump...

“There is nobody better prepared, if the president messes around with the Constitution, to handle it than Jerry Nadler,” Senate Minority Leader Charles E. Schumer (D-N.Y.) said after the vote...

“History and the precedents alike show that impeachment is not a punishment for crimes but a means to protect our constitutional system,” he said then in his opening statement during the committee’s proceedings. “And it was certainly not meant to be a means to punish a president for personal wrongdoing not related to his office.”